1. Field of the Invention
The present invention relates to a semiconductor light emitting device which generates light by emission transition using a subband level structure in a quantum well structure.
2. Related Background Art
In a conventional semiconductor laser, limits of reduction of threshold and of reduction of power consumption are determined generally according to a carrier injection rate for forming a population inversion necessary for laser oscillation. As one of the methods for exceeding the limit, a method for configuring a light emitting device by using polaritons in a resonator is considered. In a light emitting device using polaritons, by Bose-Einstein condensation (BEC), coherent light can be generated with very few injected carriers without forming a population inversion.
Here, polaritons are quasi-particles obtained by quantizing a coupled wave formed by strong coupling between an electron system and a photon system in a material. For example, when light is made incident on a material and is in a resonance state, an electron and a photon are coupled and propagate as a polariton in the material. Moreover, when the polariton propagates inside the material and reaches the material surface, it is converted into a photon with the same frequency and emitted to the outside. In addition, polaritons are bosons that obey Bose-Einstein statistics similar to photons, and therefore, the number of particles occupying a certain state can be very large (for example, refer to Patent Document 1, and Non-Patent Documents 1 and 2).    Patent Document 1: Japanese Patent Publication No. 2903017    Patent Document 2: U.S. Pat. No. 5,457,709    Patent Document 3: U.S. Pat. No. 5,745,516    Patent Document 4: U.S. Pat. No. 6,751,244    Patent Document 5: U.S. Pat. No. 6,922,427    Patent Document 6: Japanese Patent Application Laid-Open No. H8-279647    Patent Document 7: Japanese Patent Application Laid-Open No. 2008-177366    Patent Document 8: Japanese Patent Application Laid-Open No. 2008-60396    Non-Patent Document 1: R. Huang et al., “Experimental Evidence of Stimulated Scattering of Excitons into Microcavity Polaritons,” Phys. Rev. B Vol. 61 (2000) pp. R7854-R7857    Non-Patent Document 2: G. Christmann et al., “Room Temperature Polariton Lasing in a GaN/AlGaN Multiple Quantum Well Microcavity,” Appl. Phys. Lett. Vol. 93 (2008) pp. 051102-1-051102-3